Non-foreshortening stent

ABSTRACT

Self-expending stents that include circumferential rings of alternating interconnected struts connected by flexible connectors. The struts of the rings and flexible connectors have a structure, including areas of expanded or reduced width or thickness, to account for venous applications. When used for venous applications, the stents convey benefit from configurations that improve flexibility (due to the greater elasticity of venous applications) while maintaining enough stiffness to resist pressure on the venous structure in selected areas (such as for the May-Thurner syndrome). The stents include particular structural characteristics—often expressed as ratios between different measurements—that are particularly advantageous for (although not limited to) venous applications.

BACKGROUND Field of the Invention

Disclosed herein are stents for implantation within the body and methodsfor delivery and/or deployment. Certain embodiments disclosed herein maybe used in procedures to treat May-Thurner syndrome and/or deep venousthrombosis and the resulting post-thrombotic syndrome.

Description of the Related Art

May-Thurner syndrome, also known as iliac vein compression syndrome, isa condition in which compression of the common venous outflow tract ofthe left lower extremity may cause various adverse effects, including,but not limited to, discomfort, swelling, pain, and/or deep venousthrombosis (DVT) (commonly known as blood clots). May-Thurner syndromeoccurs when the left common iliac vein is compressed by the overlyingright common iliac artery, leading to stasis of blood, which may causethe formation of blood clots in some individuals. Other, less common,variations of May-Thurner syndrome have been described, such ascompression of the right common iliac vein by the right common iliacartery.

While May-Thurner syndrome is thought to represent between two to fivepercent of lower-extremity venous disorders, it frequently goesunrecognized. Nevertheless, it is generally accepted that May-Thurnersyndrome is about three times more common in women than it is in men andtypically manifests itself between the age of twenty and forty. Patientsexhibiting both hypercoagulability and left lower extremity thrombosismay be suffering from May-Thurner syndrome. To confirm that diagnosis,it may be necessary to rule out other causes for hypercoagulable state,for example by evaluating levels of antithrombin, protein C, protein S,factor V Leiden, and prothrombin G20210A.

By contrast to the right common iliac vein, which ascends almostvertically parallel to the inferior vena cava, the left common iliacvein takes a more transverse course. Along this course, it lies underthe right common iliac artery, which may compress it against the lumbarspine. Iliac vein compression is a frequent anatomic variant—it isthought that as much as 50% luminal compression of the left iliac veinoccurs in a quarter of healthy individuals. However, compression of theleft common iliac vein becomes clinically significant only if suchcompression causes appreciable hemodynamic changes in venous flow orvenous pressure, or if it leads to acute or chronic deep venousthrombosis, which will be discussed in more detail below. In addition tothe other problems associated with compression, the vein may alsodevelop intraluminal fibrous spurs from the effects of the chronicpulsatile compressive force from the overlying artery.

The narrowed, turbulent channel associated with May-Thurner syndrome maypredispose the afflicted patient to thrombosis. And, the compromisedblood flow often causes collateral blood vessels to form—most oftenhorizontal transpelvis collaterals, connecting both internal iliac veinsto create additional outflow possibilities through the right commoniliac vein. Sometimes vertical collaterals are formed, most oftenparalumbar, which can cause neurological symptoms, like tingling andnumbness.

Current best practices for the treatment and/or management ofMay-Thurner syndrome is proportional to the severity of the clinicalpresentation. Leg swelling and pain is best evaluated by vascularspecialists, such as vascular surgeons, interventional cardiologists,and interventional radiologists, who both diagnose and treat arterialand venous diseases to ensure that the cause of the extremity pain isevaluated. Diagnosis of May-Thurner syndrome is generally confirmed oneor more imaging modalities that may include magnetic resonancevenography, and venogram, which, because the collapsed/flattened leftcommon iliac may not be visible or noticed using conventionalvenography, are usually confirmed with intravascular ultrasound. Toprevent prolonged swelling or pain as downstream consequences of theleft common iliac hemostasis, blood flow out of the leg should beimproved/increased. Early-stage or uncomplicated cases may be managedsimply with compression stockings. Late-stage or severe May-Thurnersyndrome may require thrombolysis if there is a recent onset ofthrombosis, followed by angioplasty and stenting of the iliac vein afterconfirming the diagnosis with a venogram or an intravascular ultrasound.A stent may be used to support the area from further compressionfollowing angioplasty. However, currently available stenting optionssuffer from several complications—including severe foreshortenting, lackof flexibility (which can force the vessel to straighten excessively),vessel wear and eventual performation, increased load on and deformationof the stent causing early fatigue failure, and/or impedence of flow inthe overlying left iliac artery potentially causign peripheral arterialdisease. The compressed, narrowed outflow channel present in May-Thurnersyndrome may cause stasis of the blood, which an important contributingfactor to deep vein thrombosis.

Some patients suffering from May-Thurner syndrome may exhibit thrombosiswhile others may not. Nevertheless, those patients that do notexperience thrombotic symptoms may still experience thrombosis at anytime. If a patient has extensive thrombosis, pharmacologic and/ormechanical (i.e., pharmacomechanical) thrombectomy may be necessary. Thehemostasis caused by May-Thurner syndrome has been positively linked toan increased incidence of deep vein thrombosis (“DVT”).

Deep vein thrombosis, or deep venous thrombosis, is the formation of ablood clot (thrombus) within a deep vein, predominantly in the legs. Theright and left common iliac are common locations for deep veinthrombosis, but other locations of occurrence are common. Non-specificsymptoms associated with the condition may include pain, swelling,redness, warmness, and engorged superficial veins. Pulmonary embolism, apotentially life-threatening complication of deep vein thrombosis, iscaused by the detachment of a partial or complete thrombus that travelsto the lungs. Post-thrombotic syndrome, another long-term complicationassociated with deep venous thrombosis, is a medical condition caused bya reduction in the return of venous blood to the heart and can includethe symptoms of chronic leg pain, swelling, redness, and ulcers orsores.

Deep vein thrombosis formation typically begins inside the valves of thecalf veins, where the blood is relatively oxygen deprived, whichactivates certain biochemical pathways. Several medical conditionsincrease the risk for deep vein thrombosis, including cancer, trauma,and antiphospholipid syndrome. Other risk factors include older age,surgery, immobilization (e.g., as experienced with bed rest, orthopediccasts, and sitting on long flights), combined oral contraceptives,pregnancy, the postnatal period, and genetic factors. Those geneticfactors include deficiencies with antithrombin, protein C, and proteinS, the mutation of Factor V Leiden, and the property of having a non-Oblood type. The rate of new cases of deep vein thrombosis increasesdramatically from childhood to old age; in adulthood, about 1 in 1000adults develops the condition annually.

Common symptoms of deep vein thrombosis include pain or tenderness,swelling, warmth, redness or discoloration, and distention of surfaceveins, although about half of those with the condition have no symptoms.Signs and symptoms alone are not sufficiently sensitive or specific tomake a diagnosis, but when considered in conjunction with known riskfactors can help determine the likelihood of deep vein thrombosis. Deepvein thrombosis is frequently ruled out as a diagnosis after patientevaluation: the suspected symptoms are more often due to other,unrelated causes, such as cellulitis, Baker's cyst, musculoskeletalinjury, or lymphedema. Other differential diagnoses include hematoma,tumors, venous or arterial aneurysms, and connective tissue disorders.

Anticoagulation, which prevents further coagulation but does not actdirectly on existing clots, is the standard treatment for deep veinthrombosis. Other, potentially adjunct, therapies/treatments may includecompression stockings, selective movement and/or stretching, inferiorvena cava filters, thrombolysis, and thrombectomy.

In any case, treatment of various venous maladies, including thosedescribed above, can be improved with stents. Improvements in stents forvenous use are therefore desired.

BRIEF SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to an intravascular stentthat obviates one or more of the problems due to limitations anddisadvantages of the related art. Disclosed herein are self-expendingstents that include circumferential rings of alternating interconnectedstruts connected by flexible connectors. For example, the inventors havedesigned the struts of the rings and flexible connectors with structure,including areas of expanded or reduced width or thickness, to accountfor venous applications. As another example, the inventors haverecognized that venous applications benefit from configurations thatimprove flexibility (due to the greater elasticity of venousapplications) while maintaining enough stiffness to resist pressure onthe venous structure in selected areas (such as for the May-Thurnersyndrome). To that end, inventions disclosed herein include particularstructural characteristics—often expressed as ratios between differentmeasurements—that the inventors have determined are particularlyadvantageous for (although not limited to) venous applications.

In one embodiment, a stent defines a lumen having a longitudinal axis.The stent includes a plurality of cylindrical rings and flexibleconnectors. The cylindrical rings are spaced along the longitudinalaxis. Each of the cylindrical rings includes a plurality of strutsinterconnected to form alternating apexes and troughs. Each of thestruts has a main strut width and an apex strut width. The flexibleconnectors extend between adjacent pairs of the cylindrical rings. Eachof the flexible connectors includes a main connector width, an apex, anapex connector width and a pair of ends. Each of the pair of ends isconnected to one of the struts of the cylindrical rings between theapexes of the strut. The stent also includes a strut ratio of the apexstrut width to the main strut width. A connector ratio is included ofthe apex connector width to the main connector width. In one embodiment,the strut ratio is 50% to 95% and the connector ratio is 50% to 95%.

In another embodiment, each of the flexible connectors includes aconnection location ratio of 60% to 90% of a length of the strut towhich the end is connected. In other embodiments, the strut ratio may be60% and up to and including about 80%. The connection location ratio maybe about 83%.

In other embodiments, the flexible connectors may have a length of 1.3mm to 2.25 mm, including a length of about 1.7 mm. The length of each ofthe flexible connectors may be between 77% and 130% a length of thestrut to which the end is connected, such as a length the same (100%) ofthe strut to which it is connected.

In other embodiments, the flexible connectors have different shapes,such as a V-shape and an S-shape.

In another embodiment, the ends of the flexible connectors may connectto circumferentially offset struts. Also, the may be circumferentiallyoffset by at least one intervening apex.

Another embodiment includes a method of delivering the stent. The methodincludes crimping a stent onto a catheter including radially compressingand lengthening a plurality of rings connected by flexible connectors.Also, the method includes expanding the stent by expanding the rings toan enlarged diameter resulting in a shorter axial length of the rings.Also, avoiding foreshortening of the stent upon expansion by lengtheningthe connectors via a connector ratio of an apex connector width to amain connector width of 50% to 95%.

Avoiding foreshortening can also include reducing shortening of therings via a strut ratio of an apex strut width to a main strut width of50% to 95%. Further, the method can include delivering the stent into avein and deploying the stent out of the catheter with near zeroforeshortening. Avoiding foreshortening can further include use of aconnection location ratio of 60% to 90% of a length of a strut to whichan end of the flexible connector is connected.

Other embodiments of the invention include any of the ranges (or pointswithin the ranges) alone and in combination with each other disclosedherein in FIGS. 13 and 14. For example, the ratio ranges (expressed inpercentages rather than fractions) are from about 65% to 91% forconnector attachment location ratio, 70% to 108% for connector lengthratio, 62% to 94% for strut-apex width ratio and 60% to 91% forconnector-apex width ratio. Tighter ranges include 77% to 88% forconnector attachment location ratio, 92% to 99% for connector lengthratio, 76% to 86% to for strut-apex width ratio and 72% to 80% to forconnector-apex width ratio. Notably also, those ranges where they fallbelow the baseline stent line (about 2% foreshortening) haveparticularly reduced foreshortening.

For another example, the larger range ratios include a connector lengthratio from 80% to 112%, connector location attachment ratio from 66% to90%, strut-apex width ratio from 67% to 95% and connector-apex widthratio from 66% to 92%. The tighter range ratios include a connectorlength ratio from 92% to 101%, a connector location attachment ratiofrom 76% to 84%, strut-apex width ratio from 80% to 88% andconnector-apex width ratio from 75% to 82%.

In other embodiments, the ranges disclosed above are further limited tobe below the baseline stent 2% foreshortening line on FIGS. 13 and 14.

Further embodiments, features, and advantages of the intravascularstent, as well as the structure and operation of the various embodimentsof the intravascular stent, are described in detail below with referenceto the accompanying drawings.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory only,and are not restrictive of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying figures, which are incorporated herein and form part ofthe specification, illustrate an intravascular stent. Together with thedescription, the figures further serve to explain the principles of theintravascular stent described herein and thereby enable a person skilledin the pertinent art to make and use the intravascular stent.

FIG. 1 shows an inferior-posterior view of the L5 lumbar and thebifurcations of the abdominal aorta and inferior vena cava;

FIG. 2 shows a schematic of the standard overlap of the right commoniliac artery over the left common iliac vein;

FIG. 3 shows a cross-sectional schematic of the arterio-venous systemshown in FIG. 2 taken along the gray dotted line;

FIG. 4 shows a perspective view of a stent of one embodiment withcircumferential rings of struts connected by flexible connectors;

FIG. 5 shows an enlarged view of the stent of FIG. 4 with the stentopened up and laid flat;

FIG. 6 shows a further enlarged view of FIG. 5;

FIGS. 7-9 show mathematical models of stent rings and flexibleconnectors of different embodiments with various ranges offoreshortening;

FIG. 10 shows a schematic of a stent of another embodiment at compressedand expanded configurations;

FIG. 11 shows a schematic of structure of a stent of another embodimentwith an S-shaped flexible connector;

FIG. 12 shows a schematic of structure of yet another stent of anotherembodiment with flexible connectors extending between non-adjacent ringapexes;

FIG. 13 shows the interplay between various non-dimensional ranges ofthe stent structures of various embodiments designed for venous andsimilar applications; and

FIG. 14 shows the interplay between various non-dimensional ranges ofthe stent structures of various other embodiments, including the stentstructure of FIG. 12, designed for venous and similar applications.

DETAILED DESCRIPTION

The inventors have observed certain problems in the prior art associatedwith foreshortening of stents, and in particular foreshortening ofstents used for venous applications. Open-cell designed stents includerings connected together with bridge or connector struts. Closed celldesigns, such as braided stents, include more of a mesh along thelength. In either open or closed cell designs, there includes aninherent amount of foreshortening that occurs. Open cell designs canforeshorten 15-25%, depending on how the connectors are designed, andclosed cell can foreshorten as much as 50%.

Foreshortening causes difficulty in accurately placing the stent in thepatient's lumen, since the end which exits the delivery system firstwill either move the lumen or move in the lumen, toward the constrainedend during the deployment. Additionally, this movement can cause traumato the already compromised/fragile lumen being treated.

Accurate placement is ideal in all medical interventions, but it isvital in areas where the end that is first deployed is critical. Suchareas include at vessel bifurcations and branch vessels, so that theimplant does not enter or interfere with the portion of the vessel thatdoes not require treatment. Such a bifurcation is present at theinferior vena cava where it branches into right and left iliac veins, asdescribed in more detail below. May-Thurner syndrome, or iliac veincompression syndrome, occurs in the peripheral venous system when theiliac artery compresses the iliac vein against the spine as shown inFIG. 1. FIG. 1 illustrates a vertebra, the right and left common iliacarteries near the bifurcation of the abdominal aorta, and the right andleft common iliac arteries near the bifurcation of the inferior venacava. The bifurcations generally occur near the L5 lumbar vertebra.Thus, it can be seen that FIG. 1 shows an inferior-posterior view of theL5 lumbar and the bifurcations of the abdominal aorta and inferior venacava.

As shown, the strong right common iliac artery has compressed the iliacvein causing it to become narrowed. This is one possible, if not aclassic, manifestation of May-Thurner syndrome. Over time, suchnarrowing may cause vascular scarring which can result in intraluminalchanges that could precipitate iliofemoral venous outflow obstructionand/or deep vein thrombosis. As discussed above, venous insufficiency(i.e., a condition in which the flow of blood through the veins isimpaired) can ultimately lead to various deleterious pathologiesincluding, but not limited to, pain, swelling, edema, skin changes, andulcerations. Venous insufficiency is typically brought on by venoushypertension that develops as a result of persistent venous obstructionand incompetent (or subcompetent) venous valves. Current treatments forvenous outflow obstruction include anticoagulation, thrombolysis,balloon angioplasty and stenting.

FIG. 2 illustrates the standard overlap of the right common iliac arteryover the left common iliac vein. The arteries shown include theabdominal aorta 1500 branching into the left common iliac artery 1501and the right common iliac artery 1502. The veins shown include theinferior vena cava 1503 branching into the left common iliac vein 1504and right common iliac vein 1505. It will be understood that the roughdiagram illustrated in FIG. 2 represents the view looking down on apatient laying face-up (i.e., an anterior-poster view of the patient atthe location of the bifurcation of the abdominal aorta 1500 and theinferior vena cava 1503). The overlap of the right common iliac artery1502, which is relatively strong and muscular, over the left commoniliac vein 1504 can cause May-Thurner syndrome by pressing down on thevein 1504, crushing it against the spine, restricting flow, and,eventually, causing thrombosis and potentially partially or completelyclotting off of the left common iliac vein 1054 and everything upstreamof it (i.e., the venous system in the left leg, among others).

FIG. 3 illustrates a cross-section of the arterio-venous system shown inFIG. 2 taken along the gray dotted line. Shown in schematic are theright common iliac artery 1600, the left common iliac vein 1601, and avertebra 1602 of the spine (possibly the L5 lumbar vertebra of thelumbar spine). As can be seen, the right common iliac artery 1600 issubstantially cylindrical, due to its strong, muscular construction(among other potential factors). That strong, muscular artery haspressed down on the left common iliac vein 1601, until it has almostcompletely lost patency, i.e., it is nearly completely pinched off. Itwill be understood that May-Thurner syndrome may indeed involve suchsevere pinching/crushing of the underlying left common iliac vein 1601against the vertebra 1602 of the lumbar spine. However, it will also beunderstood that May-Thurner syndrome may involve much lesspinching/crushing of the underlying left common iliac vein 1601 againstthe vertebra 1602. Indeed, embodiments disclosed herein are appropriatefor the treatment of various degrees of May-Thurner syndrome, includingfull crushing/pinching of the left common iliac vein 1602 by the rightcommon iliac artery 1600. Other embodiments disclosed herein areappropriate for the treatment of various degrees of May-Thurnersyndrome, including, but not limited to a crush/pinch of the underlyingleft common iliac vein 1601 of between about 10-95%, about 15-90%, about20-85%, about 25-80%, about 30-75%, about 35-70%, about 40-65%, about45-60%, and about 50-55%, or any other crush/pinch that could merittreatment using one or more of the devices disclosed herein.

Generally, disclosed herein are self-expending stents that includecircumferential rings of alternating interconnected struts connected byflexible connectors. For example, the inventors have designed the strutsof the rings and flexible connectors with structure, including areas ofexpanded or reduced width or thickness, to account for venousapplications. As another example, the inventors have recognized thatvenous applications benefit from configurations that improve flexibility(due to the greater elasticity of venous applications) while maintainingenough stiffness to resist pressure on the venous structure in selectedareas (such as for the May-Thurner syndrome). To that end, exploredherein are particular structural characteristics—often expressed asratios between different measurements—that the inventors have determinedare particularly advantageous for (although not limited to) venousapplications.

In one embodiment shown in FIGS. 4-7, a stent 10 of the presentinvention includes a plurality of rings 12 connected by a plurality ofconnectors 14. The rings 12 are arranged in a spaced relationship alonga long axis 16 of the stent 10. The connectors 14 extend betweenadjacent pairs of the rings 12. Each of the rings and connectors arecomprised of a plurality of interconnecting struts. The dimensions andorientation of these struts are designed to provide flexibility andradial stiffness in combination with substantially reduced or, forpractical purposes in venous applications, “zero” foreshortening that isin particular advantageous for use in venous applications.

Notably the stents herein are not necessarily limited to venousapplications unless specifically required by the claims. The disclosedstents could be employed in arterial and biliary applications, forexample. But, are particularly suited for the demands of relatively softstructures defining lumens that are subject to much greater bending,twisting, stretching and other contortions and loads than are generalatrial lumens.

Each of the rings 12 is comprised of a plurality of ring struts 18interconnected to form alternating peaks or apexes 20 and troughs 22. Asshown in FIG. 6, each of the ring struts 18 is generally straight andhas a main strut width 24 and a strut length 26. The main strut width 24is the width of the strut in the circumferential direction but adjustedto be at about a right angle to the edge of the strut. In other words,the main strut width 24 is an edge to edge measurement corresponding tothe outermost circumferential surface of the struts of the rings 12.

It should be noted that terms such as perpendicular, thickness and otherdimensional and geometric terms should not be regarded as strict orperfect in their application. Instead, geometric and other dimensionalreference terms should be interpreted based on their correspondence toaccepted manufacturing tolerances and functional needs of the stent 10on which they are employed. For example, the term “perpendicular” shouldbe appreciated as affording a reasonable amount of angular variation dueto manufacturing imperfections or the actual intentional curves cut orformed in the stent design 10. Also, any thickness, width or otherdimension should be assessed based on tolerances and functional needs ofthe design rather than idealized measurements.

The thickness 28 of the strut, on the other hand, is its depth in theradial direction which is generally perpendicular to the strut widthmeasurement, as shown in FIG. 4. The strut thickness 28 normallycorresponds to the wall thickness (outside diameter minus insidediameter) of the tube from which the stent 10 is laser cut afteretching, grinding and other processing. But, embodiments of the stentsdisclosed herein are not necessarily limited to being laser-cut from acylindrical tube with a predetermined wall thickness. They could also beformed or cut from flat sheets that are welded together at long edges toform a tube-like structure.

In the embodiment shown in FIG. 6, the ring struts 18 have a relativelyconsistent or constant width 24 in between the apexes 20 and troughs 22.Similarly, the ring strut thickness 28 is relatively constant along itslength between the apexes 20 and troughs 22. The width and thickness ofthe ring struts could, however, vary along the length of the struts. Inwhich case a “main” strut width would be at least the minimum of thewidths between the apexes and troughs assuming uniform material strengthalong the strut. Generally, then, the main strut width is the width atwhich the strut has its greatest functional flexibility. Usually, forhomogenous material properties, the main strut width will be the minimumstrut width. However, the main strut width may be located at a widerportion if the material were configured to be generally less stiff thanthicker regions even at greater widths.

In some embodiments, the ring struts 18 have some change in width as theapproach the apexes 20 or the connectors 14. For example, struts in FIG.6 taper somewhat as they enter the troughs 22. Tapering can, forexample, improve clearance for compression of the ring struts 18 againsteach other in a crimping operation. Conversely, in some (or the same)embodiments, the ring strut widths increase as they approach theconnectors 14. For example, as shown in FIG. 6, the ring strut enlargeswhere the connector 14 merges with the strut and on the side of the ringstrut opposite the merging connector, the strut enlarges somewhat. Thus,the ring struts 18 enlarge a bit on both sides proximate the merging endof a connector 14.

As shown in FIGS. 5 and 6, the rings 12 are formed with alternatingapexes 20 and troughs 22 because the struts are arranged havingconnected ends in a “zigzag” pattern. Restated, each of the apexes ispaired with a corresponding trough on the opposite longitudinal side ofthe two adjacent, intersecting struts 18 and apexes and troughsalternate in the circumferential direction. Also notable is that eachpair of apexes 20 on adjacent rings (connected by the connectors 14)extend in the longitudinal direction further than the next,circumferentially adjacent pair of apexes that are not connected byconnectors 14. An advantage of this arrangement is that the two furtherpeaks provide clearance for the circumferentially pointing connectors14, especially in a compressed configuration. Also, the longitudinallycloser apexes 20 provide additional length for supporting the connectors14. In any case, the amplitude of the apexes 20 can be varied inembodiments to address different functional or geometric requirements.In the illustrated embodiment of FIGS. 5 and 6, the troughs 22, becauseof the extended peaks 20 at the connectors, are deeper on the oppositeside of those higher amplitude peaks and shallower (in the longitudinaldirection) opposite the non-connected peaks of the rings 12.

The apexes 20 are formed of the intersection of each of the ring struts18 and, in some embodiments, have a curved structure where the strutschange direction to extend back on themselves in the longitudinaldirection, as shown in FIG. 6. The struts 18 (which are part of thestruts formed into connections) at the apexes 20 of the ring struts 18have an apex width 30 that is the smallest width of the apex in the spanbetween the ends of the relatively straighter portions of the struts 18.Generally, as shown in the illustrated embodiments, the apex strut width30 of the ring struts 18 is relatively constant. But, the apex strutwidth 30 of the ring struts 18 can vary, depending upon the desiredvariation in flexibility or material stiffness, for example, along itslength.

As shown in FIGS. 4-6, the plurality of connectors 14 has a generallyV-shape and extends between adjacent, facing apexes 20 of the adjacentrings 12. For the embodiment of FIGS. 4-6, the connectors 14 connectalternate peaks, but the frequency of such connections can be varieddepending on desired flexibility of the stent 10 with recognition thattoo few connectors 14 could result in fish scaling or other bendinganomalies that would interfere with effective function. In any case,other examples of connector shape and frequency and connection locationare described hereinbelow to illustrate that such variations arepossible and still within the scope of the present invention.

Each of the connectors 14 itself is comprised of a plurality (e.g., apair) of connector struts 34, an end 32 of each connector strut 34connects to a respective ring strut 18. Each connector strut 34 in aplurality extends from its end that is connected to the respective ringstrut 18 in a respective ring 12 to a shared apex 40 so as to form theV-shape. The connector struts 34—similar to the ring struts 18 of theexemplary embodiment—have a relatively constant width except where theyconnect to the rings 12. As with the ring struts 18 described above, thewidth of the connector struts 34 enlarge somewhat as they merge intoconnections with the rings 12. The connector struts 34, advantageouslyaccounting for some of the increased stresses in the connection regions.

As shown in FIG. 6, for example, each of the connectors 14 also includesa main connector width 36 (between arrows) and an apex connector width38 (between arrows). The main connector width 36 is the width of theconnector strut 34, usually the minimum width or width expressing thearea of highest flexibility, of the strut between the rings 12 and theconnector apex 40. The apex connector width 38, as also labelled forexample on FIG. 6, is the width of the connector apex 40 somewhere alongits bend, such as in the middle of the bend. In any case, the apexconnector width 38 can be a structural expression of an area of highflexibility on the connector apex 40.

Notably, in one embodiment, the connectors 14 do not connect directly toor at the apexes 20 of the rings 12. Instead, they are offset somewhatalong the length of the ring struts 18 to which they are connected.Another meaningful metric for the structure of the stent 10 is thelocation of the connection of the ends 32 of the connectors 14 along thetotal strut length 26, as shown in FIG. 6. Each of the ends 32 of theconnectors 14, for example, connects some connector distance 42 from theopposite apex 20 (the apex on the other end of the ring strut 18) thatis less than the total distance between apexes (as measured from theiroutside radial surface) representative of the total strut length 26. Themetric, therefore, can be in the form of the ratio of the distance ofthe connector to the opposite end, as compared to the total strut length26. Thus, a connection at the apex 20 would be 100% and a connection inthe middle of the strut would be 50%.

The connectors 14 may also be expressed or described as a ratio of theiroverall length (or in the case of connectors with an apex, the lengthbetween an end of the connector and the apex—such as ½ the total lengthfor V-shaped strut of FIG. 6) compared to a baseline such as 1.7 mm inthe illustrated embodiments. A different baseline could be used fordifferent embodiments. The baseline for the ratio, for example, may alsobe a proportion of 30% to 50% the length of the ring struts 18. (In theillustrated embodiment, for example, the ring strut length can be about3.4 mm yielding a baseline, using the 50% proportion, of 1.7 mm.)

In any case, the ratio of the connector length to the baseline can be,in embodiments, about 30% shorter (70% of the baseline) or longer (130%of the baseline). A longer connector 15 that is 2.25 mm is about 130% ofthe baseline 1.7 mm and 1.3 mm is only about 77% of the baseline 1.7 mmlength. Generally, longer connectors are more flexible and thereby canprovide more mediation of shortening of the rings 12 on expansion. Buttheir length also can reduce the radial stiffness of the stent 10,resulting in an overall undesirable tradeoff. (Strut length measurementscan also vary somewhat and be measured from apex 20 to trough 22 or (asillustrated in FIG. 6) apex-to-apex.)

The inventors have redesigned the accepted prior art “typical” stent soas to improve (lessen) its foreshortening characteristics withoutconcomitant equal loss in radial stiffness by assigning and modifyingfour or five parameters or metrics of the stent 10. Although othermetrics are possible and can have some effects, the inventors havedetermined through design and testing these metrics can be arranged inparticularly effective combinations as expressed by the graphicaldepiction in FIG. 13. FIG. 13 is an X-Y line graph with the verticalaxis indicating the amount of foreshortening as a ratio of shortenedamount divided by the original, unexpanded length of the stent 10. Thehorizontal axis expresses the non-dimensional (mm/mm) ratio of theparticular parameters.

The parameters illustrated in FIG. 13 are connector length, connectorattachment location ratio, strut to apex width ratio, and connector toconnector-apex width ratio. Using the expression of connector lengthdescribed above with respect to 1.7 mm, connector length in FIG. 13 isexpressed as a ratio to the baseline embodiment stent connector lengthof 1.7 mm. For example, a 1.7 mm long connector is expressed as a “1” inthe graph. Strut to apex width is the ratio of the apex strut width 30divided by the main strut width 24. Connector width is the ratio of theapex connector width 38 to the main connector width 36. Further,connector location is expressed as a ratio of the connector distance 42divided by the strut length 26. In other words, connector location is anexpression of how far away from the apex 20 of the ring strut 18 theconnector end 32 is attached. (Most typical struts have connectorsconnecting at the apexes 20 of the rings 12, hence the ratio “1” of atypical stent.)

The inventors have designed ranges that work particularly well forvenous applications, such as those shown in FIG. 13 within the twoellipses. The outer ellipse represents a first set of collected rangesof connector location, apex width, connector width and connector lengthratios that yield foreshortening ranges, flexibility and radialstiffness that have improved outcomes for venous applications. The innerellipse represents a second, tighter set of ranges for further improvedcharacteristics that have better outcomes for venous applications. A“baseline stent” threshold is also provided graphically such that astent with parameters below the threshold line would—for treatmentpurposes—be considered a zero foreshortening stent (about 2% or lessforeshortening). The lines associated with each of the ratios show theinterplay between a particular changing parameter and the impact onforeshortening.

Referring again to FIG. 13, which is most applicable to stent geometrieswith rings and flexible connectors having at least one apex andconnecting adjacent peaks of the rings, such as shown in FIGS. 4-11, theratio ranges (expressed in percentages rather than fractions) are fromabout 65% to 91% for connector attachment location ratio, 70% to 108%for connector length ratio, 62% to 94% for strut-apex width ratio and60% to 91% for connector-apex width ratio. Tighter ranges include 77% to88% for connector attachment location ratio, 92% to 99% for connectorlength ratio, 76% to 86% to for strut-apex width ratio and 72% to 80% tofor connector-apex width ratio. Notably also, those ranges where theyfall below the baseline stent line have particularly reducedforeshortening.

In various other embodiments, ranges of the parameters include a strutratio of the apex strut width to the main strut width of 50% to 95%along with a connector ratio of the apex connector width to the mainconnector width of 50% to 95%. The inventors determined these rangesreduce foreshortening of the stent along the longitudinal axis uponradial expansion. Also, the connection location ratio can be about 60%to 90% of a length of the strut to which the end is connected.

Particularly effective ratios were determined to be a strut ratio of 60%up to and including about 80%. The connector ratio can be about 75% andthe connection location ratio about 83% for a preferred stent thatbalances flexibility, radial stiffness and constrained foreshortening.According to principles of some embodiments of the present invention,flexible connector lengths for venous applications may range from 1.3 mmto 2.25 mm with a good performance found at 1.7 mm. Also according toprinciples of some embodiments, the length of each of the flexibleconnectors may be within 77% to 130% of a length of the supportingstrut, and good performance demonstrated at the same (100%) length.

Embodiments of the stents disclosed herein include advantages such as areduction of the typical 20% to 50% of foreshortening of conventionalflexible stents, resulting in more accurate sizing and placement.Generally, the stent designs can include open celled designs thatinclude connector or bridge members that expand in length as the ringsshorten. Thus, foreshortening is reduced or avoided while the ringstiffness is preserved for vessel treatment. Design features thatfacilitate avoidance of shortening include attaching the connectors awayfrom the apexes. As shown in FIG. 10, in this position, thestrut-connector junction rotates as the ring expands. Also, theconnectors are angled such that during ring expansion the angle of theconnector decreases with the increasing angle of the strut. Decreasingconnector angle causes the distance between rings 12 to increaseoffsetting foreshortening from increasing ring strut angle.

As shown in FIG. 7, a typical stent foreshortens 15% with the stressesin the ring struts being the heaviest at the apexes 20 undergoing thelargest amount of bending. (The top of the figure shows the unstressedcompacted strut and the bottom shows the ring strut expanded andshortened by 15%.) The rigidity and orientation of the ring struts 18contribute to the shortening—their zigzag orientation resulting in anaccordion effect. FIG. 8 shows a stent that would hinge at apexes 20 andall of the translation occurs via increasing length at the connector tooffset shortening of the rings struts 18, with a net zeroforeshortening. FIG. 9 shows a stent wherein the radial stiffness withstrong and/or wide apexes 20 that is balanced with a length increase inthe connectors—but with a resulting 5% foreshortening.

To deploy the implant, the implant may be radially compressed/crimped toa smaller diameter for loading onto/into a delivery catheter. Theimplant may be crimped over a balloon on the inner core of the deliverysystem which may be later inflated to expand the coiled implant to thedesired diameter. The engagement fingers are pre-configured at specificlocations to allow discrete incremental expansion of the stent. In someembodiments, the implant can be expanded in 0.5 mm increments. In someembodiments more than one implant may be joined together. For example,the ultimate length of the implant can be controlled by joining anydesired number of individual adaptive diameter cells via flexible orrigid bridge members.

Implants such as those described above may be advantageously provide anadaptive diameter and/or flexibility to conform the dynamic movement ofperipheral veins in leg/pelvis thereby facilitating treatment of bothiliac vein compression syndrome and ilio-femoral venous outflowobstructions.

It may be desirable to have a stent that will conform to the existingpath of a vein instead of a straightening out of the vessel by thestent. It may also be desirable to have a high radial stiffness of thestent to resist collapse of the stent under crushing load and tomaximize the resultant diameter of the treated vessel at the location ofthe stent deployment. With most stent constructions there is a directrelationship between radial stiffness and axial stiffness.

Common commercially available balloon expandable stents experience adramatic change in length as a balloon is used to expand the stentwithin the vessel. Common commercially available self-expanding stentsexperience a change in length less dramatic, but still substantial,which increases with increasing stent length. Change in length betweenthe configuration within the delivery system and when deployed in thevessel causes difficulty in placing/landing the stent precisely at thetarget location. When the stent is deployed in its crimped configurationand expanded, the shortening in length causes the stent targetdeployment location to have to offset from the target dwell location.The magnitude of this effect is not controllable or easily anticipatedas it is dependent on the luminal cross-section along the length of thetarget dwell location (which is frequently and unexpectedly influencedby residual stenosis, irregular shape due to external objects, and/orforces, etc.). For target lesions leading up to the junction of the leftand right iliac into the IVC, this causes difficulty in placing thestent to dwell completely within the iliac along its total length up tothe junction to the inferior vena cava without crossing into theinferior vena cava.

In some embodiments a venous stent with high radial force, no impactfulforeshortening along multiple lengths, and high flexibility/vesselconformity is provided. Minimization of foreshortening allows the stentadvantageously accurate and predictable deployment. And, highflexibility maximizes the fatigue life of the stent under bending. Ofcourse, it will be understood that the stent may find applications inthe arterial system as well.

FIGS. 11 and 12 illustrate various views of other embodiments of a stent10 or stents configured to minimize foreshortening while retainingflexibility. FIG. 11 shows an S-shaped connector 14. For this S-shape,the two ends of the connectors attach to opposite sides of the opposingrings 12. Because of the additional apexes 40 in the connectors 14,there is additional flexibility afforded by the S-shape to counteractforeshortening of the rings. To that extent, the ratios then of apex tomain connector width can be less than that of the single apexconnectors. Additionally, the connectors 14 (of either configuration)could be designed such that in the crimped configuration, they are incontact with one another in a manner that pulls the rings together bythe amount that the individual rings foreshorten during deployment.

FIG. 12 shows a stent 10 with a plurality of rings 12 with curvedconnectors 14 that have ends 32 connected to non-opposing apexes 20 ofthe rings. In particular, the illustrated embodiment connects to everythird one of the apexes 20 and extends circumferentially in a slights-curve. The connectors 14 connect apexes that are separated by anintervening apex, thus skipping the opposite apex and the apex adjacentto that opposite apex for a third apex. Thus, additional lengthening ofthe connectors 14 is facilitated by not only offsetting from the peak,but offsetting to a different apex. This feature could be combined withthe other features disclosed herein to further mediate ringforeshortening.

FIG. 14, like FIG. 13, shows ratios that work particularly well forstents with rings and connectors connecting non-adjacent peaks, such asis shown in FIG. 12. As applied to the embodiment of FIG. 12, thestrut-apex width, connector-apex width, and connector attachmentlocation ratios are calculated the same way as for FIG. 13. But, theconnector length is calculated differently for FIG. 12. The connectorlength in this embodiment is the total length of the connector from apexto apex. For the embodiment of FIG. 6, the connector length is from theconnection 32 to the apex 40 or half the total overall length of theconnector. As above, the longer the connector length, the moreforeshortening is reduced. Also, the further the connector is attachedalong the length of the strut, the more foreshortening is minimized. Thelarger range ratios include a connector length ratio from 80% to 112%,connector location attachment ratio from 66% to 90%, strut-apex widthratio from 67% to 95% and connector-apex width ratio from 66% to 92%.The tighter range ratios include a connector length ratio from 92% to101%, a connector location attachment ratio from 76% to 84%, strut-apexwidth ratio from 80% to 88% and connector-apex width ratio from 75% to82%. As with FIG. 13, the longer the connector length, the more thatforeshortening is minimized. Also as with FIG. 13, the further theconnector is attached along the length of the strut, the moreforeshortening is minimized.

Embodiments disclosed herein can be used for both balloon expandable andself-expanding stent designs. The stent designs can be used for allstent interventions, including coronary, peripheral, carotid, neuro,biliary and, especially, venous applications. Additionally, this couldbe beneficial for stent grafts, percutaneous valves, etc.

Some embodiments disclosed herein, such as those shown in FIGS. 4-6, and8-12, decouple the relationship between radial stiffness and axialstiffness through their configuration of individual one cell long ringsfixed together at the joining of the cells of each ring through thelinkage struts. This allows for maintenance of controlled spacing by thelinkage strut between the joined rings along a pathway but gives themthe freedom to orient with the axis of one ring being different than theaxis of the adjacent rings. The individual rings, with a relatively lowaxial flexibility, orient themselves largely straight along theirindividual length with the bending happening substantially along thelinkage struts which are characterized by a much higher axialflexibility. Therefore, radial force can be controlled by the width ofthe cell struts and kept independent of the axial flexibility that iscontrolled by the width of the linkage struts. Additionally, the axiallyrotated indexing position of each adjacent pair of linkage struts,creating a spiral orientation of linkage struts, ensures that the stenthas substantially similar axial flexibility regardless of angularorientation around its axis.

With each cell connected at the attachment of the struts, there is nochange in position of one cell to the adjacent cells when the stent isfully crimped and when it's fully unconstrained. Therefore, the onlyforeshortening of the stent would come from half of the leading cell andhalf of the trailing cell. Also, the foreshortening of the presentedinvention is the same regardless of stent overall length given equallyconfigured cells (increasing length by adding more rings). When thepresented invention is deployed into the iliac-inferior vena cava (asdiscussed above), the location of the stent within the delivery systemwill equal the location of the stent when deployed form the deliverysystem into the vessel. The positioning and deployment of the stent willbe the same regardless of the stent length. Therefore, a marker locatedat the connection of the cells/attachment of the struts can giveexcellent visualization and indication of the position of the stent whenin the delivery system and when deployed in the vessel.

Currently available implants are typically loaded and retained onto adelivery system in a crimped configuration and then navigated anddeployed in the desired anatomical location where they expand to theimplanted configuration. The final implanted configuration can beachieved through mechanical expansion/actuation (e.g.,balloon-expandable) or self-expansion (e.g., Nitinol). Self-expandingimplants are manufactured from super elastic or shape memory alloymaterials. Accurate and precise deployment of a self-expanding implantcan be challenging due to a number of inherent design attributesassociated with self-expanding implants. The implant may jump/advancefrom the distal end of the delivery system during deployment due to thestored elastic energy of the material. Additionally, the implant mayforeshorten during deployment due to the change in the implant diameterfrom the crimped configuration to the expanded configuration. Finally,physiological and anatomical configurations, such a placement at or nearbifurcations of body lumens, can affect accurate placement of implants.Once the implant in placed within the body lumen there is potential foruneven expansion or lack of circumferential implant apposition to thebody lumen which can result in movement, migration or in certain severecases implant embolization.

In some embodiments, a self-expanding implant designed with sufficientradial force to resist constant compression of the body lumen whileproviding optimal fatigue resistance, accurate placement, and in-vivoanchoring to prevent is provided. Additionally, various methods fordeployment and implantation for treating iliac vein compression syndromeand venous insufficiency disease are provided.

In some embodiments, the implant comprises a purposely designed venousimplant intended to focally treat iliac vein compression (May-ThurnerSyndrome). The implant may be relatively short in length (˜40 mm) andmay be manufactured from self-expending Nitinol with integrated anchorfeatures to aid in accurate placement and to mitigate migrationfollowing implantation. The implant and delivery system are designed forprecise deployment and placement at the bifurcation of the inferior venacava into the right and left common iliac veins.

As another feature, the stents 10 disclosed herein can include anchormembers or eyelets 44, as shown in FIGS. 10 and 11.

Although this invention has been disclosed in the context of certainpreferred embodiments and examples, it will be understood by thoseskilled in the art that the present invention extends beyond thespecifically disclosed embodiments to other alternative embodimentsand/or uses of the invention and obvious modifications and equivalentsthereof. In addition, while a number of variations of the invention havebeen shown and described in detail, other modifications, which arewithin the scope of this invention, will be readily apparent to those ofskill in the art based upon this disclosure. It is also contemplatedthat various combinations or sub-combinations of the specific featuresand aspects of the embodiments may be made and still fall within thescope of the invention. Accordingly, it should be understood thatvarious features and aspects of the disclosed embodiments can becombined with or substituted for one another in order to form varyingmodes of the disclosed invention. Thus, it is intended that the scope ofthe present invention herein disclosed should not be limited by theparticular disclosed embodiments described above, but should bedetermined only by a fair reading of the claims that follow.

Similarly, this method of disclosure, is not to be interpreted asreflecting an intention that any claim require more features than areexpressly recited in that claim. Rather, as the following claimsreflect, inventive aspects lie in a combination of fewer than allfeatures of any single foregoing disclosed embodiment. Thus, the claimsfollowing the Detailed Description are hereby expressly incorporatedinto this Detailed Description, with each claim standing on its own as aseparate embodiment.

While various embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample only, and not limitation. It will be apparent to persons skilledin the relevant art that various changes in form and detail can be madetherein without departing from the spirit and scope of the presentinvention. Thus, the breadth and scope of the present invention shouldnot be limited by any of the above-described exemplary embodiments, butshould be defined only in accordance with the following claims and theirequivalents.

What is claimed is:
 1. A stent defining a lumen having a longitudinalaxis, the stent comprising: a plurality of cylindrical rings spacedalong the longitudinal axis, each of the cylindrical rings including aplurality of struts interconnected to form alternating apexes andtroughs, each of the struts having a strut length, a main strut width,and an apex strut width; and a plurality of flexible connectorsextending between adjacent pairs of the cylindrical rings, each of theflexible connectors including a pair of connector struts having a mainconnector width, an apex positioned between the pair of connector strutsand having an apex connector width, and a pair of ends, wherein the pairof connector struts are angled relative to one another when the stent isin a compressed configuration, and wherein each of the pair of ends isconnected to one of the struts of the cylindrical rings at a connectionlocation between the apexes of the strut; wherein a strut ratio of theapex strut width to the main strut width is 50% to 95%, wherein aconnector ratio of the apex connector width to the main connector widthis 50% to 95%, and wherein a connection location ratio of a lengthbetween the connection location and one of the apexes of the strut tothe strut length is 60% to 90% so as to reduce foreshortening of thestent along the longitudinal axis upon radial expansion; wherein theapex strut width is measured from one edge of the apex across acontinuous surface to an opposite edge of the apex, wherein the mainstrut width is measured from one generally straight edge of the strutacross a continuous surface to an opposite generally straight edge ofthe strut, wherein the one generally straight edge of the strut isparallel to the opposite generally straight edge of the strut, andwherein the continuous surface across which the main strut width ismeasured extends from one end of the strut to an opposite end of thestrut.
 2. The stent of claim 1, wherein the connection location ispositioned on the one generally straight edge or the opposite generallystraight edge.
 3. The stent of claim 1, wherein the strut ratio of theapex strut width to the main strut width is 60% to 80%.
 4. The stent ofclaim 2, wherein the strut ratio of the apex strut width to the mainstrut width is about 80%.
 5. The stent of claim 4, wherein the connectorratio is about 75%.
 6. The stent of claim 5, wherein the connectionlocation ratio is about 83%.
 7. The stent of claim 6, wherein each ofthe flexible connectors has a length of 1.3 mm to 2.25 mm.
 8. The stentof claim 7, wherein the length of each of the flexible connectors isabout 1.7 mm.
 9. The stent of claim 1, wherein the connection locationratio is about 83% and the strut ratio is about 80%.
 10. The stent ofclaim 1, wherein a length of each of the flexible connectors is between77% and 130% of a length of the strut to which the end is connected. 11.The stent of claim 1, wherein a length of each of the flexibleconnectors is 100% of the length of the strut to which the end isconnected.
 12. The stent of claim 1, wherein a length of each of theflexible connectors is about 1.7 mm.
 13. The stent of claim 1, whereineach of the flexible connectors has a V-shape with at least one apex.14. The stent of claim 1, wherein each of the flexible connectors has anS-shape with at least two apexes.
 15. The stent of claim 1, wherein theends of the flexible connectors connect to circumferentially offsetstruts.
 16. The stent of claim 15, wherein the circumferentially offsetstruts are offset by at least one intervening apex.
 17. The stent ofclaim 1, wherein each of the struts is generally straight along theentirety of a length of the strut.
 18. The stent of claim 1, whereineach of the struts is defined by a continuous body portion extendingfrom the one end of the strut to the opposite end of the strut, andwherein each of the flexible connectors is defined by a continuous bodyportion extending from one end of the flexible connector to an oppositeend of the flexible connector.
 19. The stent of claim 1, wherein theplurality of struts of each of the cylindrical rings comprises aplurality of first struts each having a first strut length and aplurality of second struts each having a second strut length, andwherein the first strut length is greater than the second strut length.20. The stent of claim 1, wherein each of the flexible connectors isconnected to one of the first struts.
 21. A stent defining a lumenhaving a longitudinal axis, the stent comprising: a plurality ofcylindrical rings spaced along the longitudinal axis, each of thecylindrical rings including a plurality of struts interconnected to formalternating apexes and troughs, each of the struts having a strutlength, a main strut width, and an apex strut width; and a plurality offlexible connectors extending between non-adjacent pairs of thecylindrical rings, each of the flexible connectors including a pair ofconnector struts having a main connector width, an apex positionedbetween the pair of connector struts and having an apex connector width,and a pair of ends, wherein the pair of connector struts are angledrelative to one another when the stent is in a compressed configuration,and wherein each of the pair of ends is connected to one of the strutsof the cylindrical rings at a connection location between the apexes ofthe strut; wherein a strut ratio of the apex strut width to the mainstrut width is 67% to 95%, wherein a connector ratio of the apexconnector width to the main connector width is 66% to 92%, and wherein aconnection location ratio of a length between the connection locationand one of the apexes of the strut to the strut length is 60% to 90% soas to reduce foreshortening of the stent along the longitudinal axisupon radial expansion; wherein the apex strut width is measured from oneedge of the apex across a continuous surface to an opposite edge of theapex, wherein the main strut width is measured from one generallystraight edge of the strut across a continuous surface to an oppositegenerally straight edge of the strut, wherein the one generally straightedge of the strut is parallel to the opposite generally straight edge ofthe strut, and wherein the continuous surface across which the mainstrut width is measured extends from one end of the strut to an oppositeend of the strut.
 22. The stent of claim 21, wherein the connectionlocation is positioned on the one generally straight edge or theopposite generally straight edge.
 23. The stent of claim 22, wherein alength of each of the flexible connectors is between 80% and 107% of alength of the strut to which the end is connected.
 24. The stent ofclaim 23, wherein the strut ratio of the apex strut width to the mainstrut width is 80% to 88% and the connector ratio is 75% to 82%.
 25. Thestent of claim 24, wherein the connection location ratio is 70% to 85%and the length of each of the flexible connectors is between 92% and101% of the length of the strut to which the end is connected.
 26. Thestent of claim 21, wherein each of the struts is generally straightalong the entirety of a length of the strut.
 27. The stent of claim 21,wherein each of the struts is defined by a continuous body portionextending from the one end of the strut to the opposite end of thestrut, and wherein each of the flexible connectors is defined by acontinuous body portion extending from one end of the flexible connectorto an opposite end of the flexible connector.
 28. The stent of claim 21,wherein each of the flexible connectors has a V-shape with at least oneapex.
 29. The stent of claim 21, wherein the plurality of struts of eachof the cylindrical rings comprises a plurality of first struts eachhaving a first strut length and a plurality of second struts each havinga second strut length, and wherein the first strut length is greaterthan the second strut length.
 30. The stent of claim 29, wherein each ofthe flexible connectors is connected to one of the first struts.